Thin film transistor liquid crystal display (TFT-LCD) devices have attracted much attention because of their characteristics such as the small size, low power consumption and no radiation. The TFT-LCD devices hold a dominant position in the field of flat displays, and are widely used in all walks of life. A liquid crystal display is usually formed by fitting a color filter substrate and an array substrate together, and in the prior art, a color resist is usually set on the color filter substrate, hence a deviation in the fitting process may cause light leakage. Color filter on array (COA) technology means that a color resist is produced on an array substrate, and the array substrate produced by the technology can effectively reduce light leakage due to the fitting deviation, whereby pixel aperture ratio can be effectively improved.
On a COA array substrate, in order to enable an ITO layer to electrically contact with a metal layer of the array substrate, it is necessary to provide contact holes on a color resist layer so that the metal layer is exposed. Thus, when an ITO layer is fabricated, the metal layer can be electrically contacted with the ITO layer by the contact holes. With diversification of product design, more and more contact holes are provided on the color resist layer. In the process of fabricating a PI alignment film, due to limitations of the existing PI alignment film equipment, that is, the minimum size of PI droplets generated from the existing equipment is 75 ng, when a PI droplet contacts the middle of the contact hole, an air bubble may be formed in the contact hole. FIG. 1a is a cross-sectional view of the prior art when an alignment film droplet drops right onto a contact hole in a B color resist layer. FIG. 1b is a schematic diagram showing positions of contact holes and positions of column-shaped spacers in the prior art when the array substrate is viewed in a normal direction thereof. FIG. 1b shows, from left to right, a red (R) color resist, a green (G) color resist, and a blue (B) color resist in sequence. Each of the three color resists is provided therein with a contact hole 35. A sub spacer generally may not abut against the array substrate, and therefore a projection of the sub spacer on the R color resist layer and the G color resist layer is a projection 15. A column-shaped spacer 63 abuts against the B color resist layer 33. As can be seen from FIGS. 1a and 1b, when a PI droplet 31 drops onto the contact hole 35 formed between the B color resist layer 33 and a metal layer 34, the PI droplet 31 cannot be distributed in the contact hole 35 due to the small size of the contact hole 35, and therefore an air bubble 32 is formed inside the PI droplet 31. As shown in FIG. 2, in a PI prebaking process, the air bubble 32 may expand and burst as temperature increases, causing the PI to accumulate around the contact hole 35, which renders a portion of a PI layer where the PI accumulates thicker than other parts of the PI layer. In a subsequent process for fabricating the column-shaped spacer, when the column-shaped spacer abuts against the thicker portion of the PI layer, it is bound to cause a larger cell gap. As shown in FIG. 3, the column-shaped spacer 63 abuts against a position 64 on the PI layer where the PI is accumulated, causing a gap H to be larger than a gap H′ at a normal display area, and thus resulting in a luminance difference and brightness strips.